Human speech is a result of the coordination among many systems of the human body, including respiratory system, articulation system, and various associated muscles and neurons. Damages to the neurons associated with those systems may result in impairment of functionalities of the systems, and difficulty in normal pronunciations, leading to unintelligible speech. Such a condition of unintelligible speech is commonly referred to as dysarthria.
It is noted that a person with the dysarthria condition usually does not have problem understanding cognitive language, and his/her attempted pronunciations of a particular word remain generally consistent.